(1) Field of the Invention
This invention relates to a brush device in a rotary electric machine such as a starter motor.
(2) Description of the Prior Art
FIGS. 1 and 2 show a conventional brush device which has been disclosed, for instance, in Published Unexamined Japanese Utility Model Application No. 181156/1985. In these figures, reference numeral 1 designates a commutator of a rotary machine; 6a, a bolt for fixing the stator of the machine to its frame; 2a and 2b, positive brushes and negative brushes, respectively; 3, brush springs; and 4, a brush holding frame which accommodates the four brushes 2a and 2b and the four brush springs 3. The positive side of the frame 4 is fixedly secured through an electrically insulating synthetic resin board 5 to an iron substrate 6 so that the frame 4 is electrically insulated from the substrate, while the negative side is fixedly connected directly to the substrate 6 by caulking. The positive brushes 2a have external lead wires 7a and 7b, respectively, which are connected to an external input lead wire 8, while the negative brushes 2b are connected through external lead wires 9 to the substrate 6. Lead wires 7a, 7b and 9 pass through side portions of the brush holding frame 4 at corresponding points, such as the points 17a, 17b and 19 illustrated in FIGS. 1 and 2.
The brush springs 3 urge the brushes 2a and 2b against the commutator 1. Further in FIG. 1, reference numeral 10 designates a connector connected to the external lead wire 8. The connector 8a is connected to a power source such as a battery (not shown).
In the above-described brush device, the brushes 2a and 2b are placed in the space or chamber 18 formed by the brush holding frame 4 and the synthetic resin boards 5 or the substrate 6. Since the frame's radially outward ends 18a are closed (as illustrated in FIG. 1), since the radially inward ends are effectively air-sealed by the brushes' contact with commutator 1, and since the points or openings 17a, 17b and 19 are effectively air-sealed by the lead wires passing therethrough, the heat generated by the brushes is not radiated outside, thus deforming the synthetic resin boards (or thermally deforming the brush holding frame).